Speed limiting systems for internal combustion engines

ABSTRACT

A speed limiting system for an internal combustion engine has a switching device in series with the primary winding of an ignition coil, a spark being produced when the switching device is turned off. The speed limiting system comprises a thyristor connected in a circuit across the primary winding and a transistor which is coupled to the switching device and is turned on as a result of opening of the switching device. Current flow is initiated to the gate of the thyristor at a predtermined instant of time after the transistor has been turned on, and is maintained for a predetermined period of time. The thyristor prevents production of a further spark if the switching device is turned off during the predetermined period of time.

Harris Dec.4, 1973 SPEED LIMITING SYSTEMS FOR INTERNAL COMBUSTION ENGINES [75] Inventor: Paul Anthony Harris, Walsall,

England [73] Assignee: Joseph Lucas (Industries) Limited,

Birmingham, England 22 Filed: June 28, 1971 21 Appl.No.: 157,252

[30] Foreign Application Priority Data 3,153,746 10/1964 Atkinson 123/102 FOREIGN PATENTS OR APPLICATIONS 2,004,464 l/197O Germany 123/148 E Primary Examiner-Laurence M. Goodridge Attorney-I-I0lman 8!. Stem 5 7 1 ABSTRACT A speed limiting system for an internal combustion engine has a switching device in series with the primary winding of an ignition coil, a spark being produced when the switching device is turned off. The speed limiting system comprises a thyristor connected in a circuit across the primary winding and a transistor which is coupled to the switching device and is turned on as a result of opening of the switching device. Current flow is initiated to the gate of the thyristor at a predtermined instant of time after the transistor has been turned on, and is maintained for a predetermined period of time. The thyristor prevents production of a further spark if the switching device is turned 05' during the predetermined period of time.

7 Claims, 3 Drawing Figures PATENTED BEE 4 I975 SHEET 10? 2 J MQL 'QL ATTORNEYS SPEED LIMITING SYSTEMS FOR INTERNAL COMBUSTION ENGINES This invention relates to speed limiting systems for internal combustion engines.

A speed limiting system according to the invention is intended for use with an internal combustion engine having an ignition coil with a primary winding and a secondary winding, means connecting said secondary winding to the plugs of the engine in turn, and an engine driven switching device through which the primary winding is connected to a dc source, the engine driven switching device being turned on and off in timed relationship to the engine and a spark being produced when said switching device is turned off to break current flow in said primary winding, said system comprising a thyristor connected in a circuit across said primary winding, -a transistor which is coupled to the switching device and is turned on as a result of opening of said switching device, means for initiating flow of gate current to the thyristor at a predetermined instant of time after the transistor has been turned on, and maintaining gate current for a predetermined period of time, and means for holding said transistor on until gate current is supplied to the thyristor, said thyristor preventing production of a further spark if said switching device is turned off during said predetermined period of time, and said predetermined instant of time being chosen so that the switching device is never turned off before said predetermined period of time commences.

In many known speed limiting systems it is necessary to measure engine speed over a number of cycles. The great advantage with such an arrangmeent is that because of the delay in speed measurement the speed can continue to increase to a dangerous level during said delay. Using the present invention, the engine speed is never actually measured, but there is automatically defined at all times a time zone, represented by said predetermined period of time, during which no further sparks can be produced. The reason for only starting to supply gate current to the thyristor at a predetermined instant of time after the previous opening of the switching device is to give the spark time to extinguish. It will be noted thatwhile the spark is extinguishing during this period, the transistor which must conduct to start each cycle is held on. By keeping this transistor on, the arrangement has the important advantage that the circuit cannot be re-triggered by signals received from the engine driven switching device. This is of particular importance where, as is usual, the engine driven switching device is a contact breaker, because when a contact breaker opens, it produces an oscillatory signal which dies away and is then followed by a further signal at a later point in the cycle. This further signal appears before the supply of gate current to the thyristor is allowed.

In the accompanying drawings,

FIG. 1 is a circuit diagram illustrating one example of the invention, and

FIGS. 2 and 3 are graphs illustrating the operation of the circuit.

Referring to FIG. 1, there are provided positive and negative supply lines'5l, 52 between which the vehicle battery 53 isconnected, the line 52 conveniently being earthed. The ignition coil of the vehicle includes a primary winding 54 which is connected in series with-a contact breaker 55 between the lines 51, 52, the contact breaker 55 being bridged by a capacitor 56 in the usual way, and the secondary winding 57 of the ignition coil being connected through a distributor 58 to the spark plugs 59 of the engine in turn.

The junction of the winding 54 and contact breaker 55 is connected through a diode 61, a resistor 62 and a resistor 63 in series to the base of an n-p-n transistor 64, the junction of resistors 62 and 63 being connected to the line 52 through a capacitor 65, and the base of the transistor 64 being connected to the line 52 through a resistor 66. The collector of the transistor 64 is connected through a resistor 67 to a supply .line 68 which is coupled to the line 51 through a resistor 69 and is earthed through a Zener diode 71. The collector of the transistor 64 is further connected to a capacitor 72 and a resistor 73 in series to the base of an n-p-n transistor 74, the junction of the capacitor 72 and resistor 73 being connected to the line 68 through a resistor 75.

The transistor 74 has its emitter connected to the line 52 and its collector connected through a resistor 76 to the line 68, and further connected through a capacitor 77 and a resistor 78 in series to the base of an n-p-n transistor 79, the emitter of which is connected to the line 52. The junction of the capacitor 77 and resistor 78 is connected to the line 68 through a resistor 81, and the collector of the transistor 79 is connected through a resistor 82 to the line 68, through a resistor to the base of the transistor 64, and through a capacitor 83 and a resistor 84 in series to the base of an n-p-n transistor 85. The junction of the capacitor 83 and resistor 84 is connected to the line 68 through a resistor 86, whilst the transistor 85 has its emitter connected to the line 52 and its collector connected through a resistor 87 and a diode 88 in series to the line 51 The junction of the resistor 87 and diode 88 is connected to the gate of a thyristor 89, the cathode of which is connected to the line 51 and its anode of which is connected to the junction of the winding 54 and contact breaker 55. The gate-anode path of the thyristor 89 is bridged by a resistor 91.

The contact breaker 55 is opened and closed in timed relationship to the engine, and when it is closed energy is stored in the winding 54. On opening the contact breaker 55, the energy stored in "the winding 54 produces a spark at the appropriate plug 59 in the usual way. The interval between successive openings of the contact breaker 55 will be dependent on the speed of the engine, and will decrease as the speed of the engine increases. The circuit is designed to prevent production of sparks when the engine speed is above a predetermined value, corresponding to the length of time between successive openings of the contact breaker 55 being below a predetermined value.

Assuming for the moment that the speed of the engine is below the predetermined value, then the circuit operates in a manner which is illustrated by FIG. 2. In FIG. 2 the first four wave forms from the top relate to the transistors 64, 74, 79 and respectively, and indicate whether the respective transistors are conducting or not conducting. The bottom waveform illustrates the gate current supplied to the thyristor 88. The instants at which the contact breaker 55 open are indicated by the numerals zero on the time scale. When the contact breaker 55 opens, the waveform at the junction of the contact breaker 55 and winding 54 is in the form of a short burst of oscillations, and these oscillations are smoothed by the diode 61 and capacitor 65 and then serve to turn on the transistor 64. vAs the contact breaker 55 opens, the transistors 74, 79 and 85 are all on and no gate current is supplied to the thyristor 88, but conduction of the transistor 64 results in current flowing through the resistor 75 being diverted by way of the capacitor 72 and the collector-emitter path of the transistor 64, so that the transistor 74 turns off as indicated in FIG. 2, and remains off for a period of time t1, which represents the time taken for the capacitor 72 to charge. Preferably, a further resistor 100 is connected between the collector of the transistor 74 and the base of the transistor 64 so that during the time t1 the transistor 64 is held on by current flowing through this additional resistor and the resistor 76. As soon as the capacitor 72 is charged, current flowing through the resistor 75 turns on the transistor 74 again, and as a result a capacitor 77 which when the transistor 74 turned off discharged through the resistor 76 and 78, starts to charge again through the collector-emitter of the transistor 74, so turning off the transistor 79. As soon as the transistor 79 turns off current flows through the resistor 82 and 80 inseries to provide base current to the transistor 64, so that the transistor 64 stays on even if no further signal is applied by way of the diode 61.

The transistor 79 stays off until the capacitor 77 has charged, and this time period is represented in FIG. 2 by :2. At the end of the period :2, the capacitor 77 is charged, and the transistor 79 turns on again. The transistor 64 can now turn off if no base current is being received from the capacitor 63. At the same time, the capacitor 83, which when the transistor 79 was turned off discharged through resistor 82 and resistor 84, starts to charge through the collector-emitter of the transistor 79, and resistor 86 so turning off the transistor 85. The transistor, 85 remains off for a period of time :3 during which the capacitor 83 charges, and then is turned on again by current flowing through the resistors 86 and 84. During the period when the transistor 85 is off, gate current can be supplied to the thyristor 89. It will of course be appreciated that by virtue of the back e.m.f. by the winding 54, the anode of the thyristor 89 will be at a considerably higher potential than the line 51 when the contact breaker 55 opens, so that the thrysistor 89 can still conduct even though its cathode is connected to the positive line. This arrangement of the thyristor 89 has the advantage that because the cathode is connected to the positive line there is no possibility of the thyristor 89 conducting if the engine stalls.

When the contact breaker 55 opens, it produces a further pulse sometime after the opening. This is a known feature of ignition systems, but it could cause some difficulty if the transistor 64 were not held on for the period of time t1+t2. The period t2 is chosen so that this additional pulse occurs during the period 12, since the circuit is so designed that the transistor 64 is intended to be conducting during this period, the additional pulse from the contact breaker has no effect.

At the end of the period t3, the circuit remains in its steady state as indicated in FIG. 2 with the transistors 74,79 and 85 all conducting. The cycle then re-starts when the contact breaker 55 opens, as clearly shown-in FIG. 2. Thus, when the circuit is operating with the engine speed below the predetermined value, the thyristor 89 can be supplied with gate current during the period of time t3, but the gate current is inhibited before the contact breaker opens again, so that the thyristor 89 plays no part in the operation of the circuit.

In order to understand the operation of the circuit when the engine speed is above the predetermined value, reference is directed to FIG. 3. At the commencement of a cycle, the transistor 64 is turned on as described above, and the operation is in fact identical for the period t1+t2. However, with the speed above the predetermined value, the contact breaker 55 will open again during the period :3. It will be understood that the periods t1, t2, and 23 are so chosen that the engine is not capable of overspeeding without ignition so that the contact re-opens within a period t1+t2.

When the contact breaker 55 opens, the thyristor 89 is supplied with gate current through resistor 91 as clearly seen in FIG. 3, and so the current in the winding 54 is maintained by way of the thyristor, and no spark is produced. However, the transistor 64 is turned on again and so another cycle re-commences, with the transistor 74 being turned on after a period tlin the new cycle, where tlis of course equal to t1. The only difference is that the transistor is now off at the beginning of the new cycle, and in fact remains off until the end of the period 13 in the previous cycle, as indicated in FIG. 3. This of course does not matter, because the transistor 85 is on again at the end of the period :2- in the new cycle, at which point it turns off to perform its function of allowing the thyristor 89 to conduct. It should be noted that although in the arrangement shown in FIG. 3 the transistor 85 remains off until the end of the period t3 in the first cycle, it is possible for the transistor 85 to turn on before this stage. Thus, at the end of the period tlin the second cycle, the transistor 79 turns off, and if the transistor 85 is still off at this stage, it will automatically turn on. Because for simplicity the periods 11, t2 and :3 have been shown as equal in FIGS. 2 and 3, it is not possible for the period tlto terminate before the period t3. However, if the time periods are not equal, which of course they are unlikely to be in practice, then the period tlcan terminate before the period t3, and so the transistor 85 will turn on again at this point in time. The operation is of course unaffected by this feature, because the important feature of the transistor 85 is that it should be nonconducting after the period t2 in the first cycle or t2- in the second cycle.

It will of course be appreciated that in FIG. 3 the third opening of the contact breaker 55 is not shown. If the engine continues to run too fast after the second opening of the contact breaker, then of course the next opening will occur during the period t3- and the waveforms drawn in FIG. 3 will be modified.

In a modification, one or more of the resistors 75, 81,86 is variable so that the three delay periods can be set to suit different requirements. The circuit can also be used when the contact breaker 55 is replaced by some form of semi-conductor device which is turned on and off by the engine.

I claim:

1. A speed limiting system for an internal combustion engine having an ignition coil with a primary winding and a secondary winding, means connecting said secondary winding to the plugs of the engine in turn, and an engine driven switching device through which the primary winding is connected to a dc. source, the engine driven switching device being turned on and off in timed relationship to the engine and a spark being produced when said switching device is turned off to break current flow in said primary winding, said system comprising a thyristor connected in a circuit across said primary winding, a transistor which is coupled to the switching device and is turned on as a result of opening of said switching device, means for initiating flow of gate current to the thyristor at a predetermined instant of time after the transistor has been turned on, and allowing gate current for a predetermined period of time, and means for holding said transistor on until gate current is supplied to the thyristor, said thyristor preventing production of a further spark if said switching device is turned off during said predetermined period of time, and said predetermined instant of time being chosen so that the switching device is never turned off before said predetermined period of time commences.

2. A system as claimed in claim 1 including a first capacitor which charges when the first-mentioned transistor is turned on, a second transistor which is held off while the first capacitor charges and is then turned on again, a feedback circuit from the second transistor to the first transistor, a second capacitor which charges when the second transistor turns on, a third transistor which is turned off when the second capacitor is charging and then turns on again, a feedback circuit from the third transistor to the first transistor, said feedback cir cuit providing the required means: for holding the first transistor on, a third capacitor which charges when the third transistor turns on again, and a fourth transistor which is turned off while the third capacitor is charging and then turns on again, the fourth transistor serving when it is off to allow gate current to be supplied to the thyristor.

3. A system as claimed in claim 2 including a feedback circuit from the second transistor to the first transistor for holding the first transistor on when the second transistor is off.

4. A system as claimed in claim 2 including means for varying the charging rate of the first capacitor.

5. A system as claimed in claim 2 including means for varying the charging rate of the second capacitor.

6. A system as claimed in 2 including means for varying the charging rate of the third capacitor.

7. A system as claimed in claim 2 in which the engine driven switching device is a contact breaker. 

1. A speed limiting system for an internal combustion engine having an ignition coil with a primary winding and a secondary winding, means connecting said secondary winding to the plugs of the engine in turn, and an engine driven switching device through which the primary winding is connected to a d.c. source, the engine driven switching device being turned on and off in timed relationship to the engine and a spark being produced when said switching device is turned off to break current flow in said primary winding, said system comprising a thyristor connected in a circuit across said primary winding, a transistor which is coupled to the switching device and is turned on as a result of opening of said switching device, means For initiating flow of gate current to the thyristor at a predetermined instant of time after the transistor has been turned on, and allowing gate current for a predetermined period of time, and means for holding said transistor on until gate current is supplied to the thyristor, said thyristor preventing production of a further spark if said switching device is turned off during said predetermined period of time, and said predetermined instant of time being chosen so that the switching device is never turned off before said predetermined period of time commences.
 2. A system as claimed in claim 1 including a first capacitor which charges when the first-mentioned transistor is turned on, a second transistor which is held off while the first capacitor charges and is then turned on again, a feedback circuit from the second transistor to the first transistor, a second capacitor which charges when the second transistor turns on, a third transistor which is turned off when the second capacitor is charging and then turns on again, a feedback circuit from the third transistor to the first transistor, said feedback circuit providing the required means for holding the first transistor on, a third capacitor which charges when the third transistor turns on again, and a fourth transistor which is turned off while the third capacitor is charging and then turns on again, the fourth transistor serving when it is off to allow gate current to be supplied to the thyristor.
 3. A system as claimed in claim 2 including a feedback circuit from the second transistor to the first transistor for holding the first transistor on when the second transistor is off.
 4. A system as claimed in claim 2 including means for varying the charging rate of the first capacitor.
 5. A system as claimed in claim 2 including means for varying the charging rate of the second capacitor.
 6. A system as claimed in 2 including means for varying the charging rate of the third capacitor.
 7. A system as claimed in claim 2 in which the engine driven switching device is a contact breaker. 